Red Giant Stars: Facts, Definition & the Future of the Sun Red Giant Stars: Facts, Definition & the Future of the Sun By Nola Taylor Redd, Space.com Contributor | August 21, 2013 06:00pm ET MORE Expanding red giant stars will swallow too-close planets. In the solar system, the sun will engulf Mercury and Venus, and may devour Earth, as well. Credit: James Gitlin/STScI AVL A red giant star is a dying star in the last stages of stellar evolution. In only a few billion years, our own sun will turn into a red giant star, expand and engulf the inner planets, possibly even Earth. What does the future hold for the light of our solar system and others like it? Forming a giant Most of the stars in the universe are main sequence stars — those converting hydrogen into helium via nuclear fusion . A main sequence star may have a mass between a third to eight times that of the sun and eventually burn through the hydrogen in its core. Over its life, the outward pressure of fusion has balanced against the inward pressure of gravity. Once the fusion stops, gravity takes the lead and compresses the star smaller and tighter.

Temperatures increase with the contraction, eventually reaching levels where helium is able to fuse into carbon. Depending on the mass of the star, the helium burning might be gradual or might begin with an explosive flash. The energy produced by the helium fusion causes the star to expand outward to many times its original size. Red giant stars reach sizes of 100 million to 1 billion kilometers in diameter (62 million to 621 million miles), 100 to 1,000 times the size of the sun today. Because the energy is spread across a larger area, surface temperatures are actually cooler, reaching only 2,200 to 3,200 degrees Celsius (4,000 to 5,800 degrees Fahrenheit), a little over half as hot as the sun. This temperature change causes stars to shine in the redder part of the spectrum, leading to the name red giant, though they are often more orangish in appearance. This picture of the dramatic nebula around the bright red supergiant star Betelgeuse was created from images taken with the VISIR infrared camera on ESO’s Very Large Telescope (VLT).

This structure, resembling flames emanating from the star, forms because the behemoth is shedding its material into space. Credit: ESO/P. Kervella Stars spend approximately a few thousand to 1 billion years as a red giant. Eventually, the helium in the core runs out and fusion stops. The star shrinks again until a new helium shell reaches the core. When the helium ignites, the outer layers of the star are blown off in huge clouds of gas and dust known as planetary nebulae . The core continues to collapse in on itself. Smaller stars such as the sun end their lives as compact white dwarfs. The material of larger, more massive stars fall inward until the star eventually becomes a supernova , blowing off gas and dust in a dramatic fiery death. [ Amazing Photos of Supernova Explosions ] Though they look serene and silent from our vantage on Earth, stars are actually roiling balls of violent plasma. Test your stellar smarts with this quiz. The End Of The Sun The End Of The Sun The Helium Flash The beginning of the end for a red giant the mass of our Sun occurs very suddenly. As the helium "ashes" continue to pile up at its center, a higher fraction of them turn electron-degenerate.

It is an odd paradox: even as the outer layers of a red giant star are expanding into a huge but tenuous cloud, its inner core is contracting down to form a buried white dwarf. The temperature and pressure in the Sun's core will soar to 10 times their current values. And roughly 1.2 billion years after it leaves the main sequence, at the height of its glory as a red giant, the center of the helium core of the Sun will become sufficiently massive, dense, and hot that something amazing will happen: within a matter of minutes, it will ignite and burn. When the temperature in the core reaches about 100 million degrees, the helium will begin to fuse into carbon by a reaction known as the triple-alpha process, because it converts three helium nuclei into one carbon atom. This generates a great deal of heat. However, unlike when the Sun was young and its core contained normal matter, adding more heat to the electron-degenerate helium does not cause it to expand and cool. As I noted when I was discussing quantum mechanics , electron-degenerate matter behaves more like a liquid than a gas when you heat it: its temperature swiftly rises, but it doesn't expand.

In other words, the self-regulating mechanism that keeps main-sequence stars so stable (hydrostatic equilibrium) is turned off in electron-degenerate matter. If you add heat to a white dwarf, it just gets hotter. As it happens, the triple-alpha process is exceptionally highly temperature dependent: doubling the temperature of the reaction causes it to run roughly a trillion times faster! So, as the fusing helium heats the core, which cannot expand to cool down, the increased temperature causes the helium fusion to suddenly proceed millions of times faster, which very rapidly heats the core even more, which in turn causes the helium to fuse way, way faster . . . In short, the center of the helium core explodes. About 6% of the electron-degenerate helium core, which by now weighs in at about 40% of a solar mass, is fused into carbon within a few minutes. (This corresponds to burning roughly ten Earth masses of helium per second, if you are keeping score.) For obvious reasons, astronomers call this the helium flash. In roughly the time it takes to toast a bagel, the flash releases as much energy as our current Sun generates in 200 million years.

At the height of the flash, the Sun's core will very briefly equal the combined luminosity of all the stars in the Milky Way galaxy! One might imagine that a conflagration of this magnitude would have a dramatic impact on the red giant – and it does, in a way, but not nearly so suddenly or violently as you might think. This is because we tend to underestimate gravity. Compared to the intimidating power of nuclear weaponry, the energy generated by dropping a few rocks doesn't seem very impressive. But in fact, the gravitational energy of extremely dense, extremely large masses is startling – it is only our human prejudice, arising from the fact that we live on a puny pebble that is neither massive nor dense, which makes us think otherwise. Navigation Menu After The Supernova Suppose we do take the Earth as an example of a large, dense object, even though it is about as dense as cotton candy when compared to a white dwarf.

To inflate the Earth to twice its size – that is, to lift the mass of the Earth against its own gravity until its radius is doubled – would require all the solar energy striking the surface of the Earth (a mere 185,000,000,000 megawatts) for the next 13 million years! During the helium flash, a star's degenerate core is heated so intensely that it finally "vaporizes", so to speak. That is, individual nuclei begin moving so fast that they can "boil away" and escape it. The core reverts back into a (spectacularly dense) normal gas, and powerfully expands. The enormous gravitational energy needed to expand 100,000 Earth masses out of degeneracy and up to several times their original volume is on a par with the energy release of the helium flash. Or in other words, almost all the energy of the flash is absorbed by the titanic weight-lifting necessary to lift the core out of its white-dwarf condition.

Essentially none of the energy reaches the surface of the red giant, and indeed, if you were observing the red giant with your naked eye as its helium core flashed over, it is doubtful that you'd notice anything at all. So, by human standards, the helium flash is a disappointing dud to watch. By galactic standards, however, the red giant has been shot through the heart. The sudden expansion of the core results in cooling so severe that it is something like the onset of an Ice Age. The cooling immediately leads to much lower pressure in the hydrogen-burning shell that surrounds the core, and therefore to a calamitous drop in the energy output. On a timescale which is almost instantaneous compared to the usual timescale that stars run on (perhaps as little as 10,000 years), the red giant's diameter and luminosity plummet to less than 2% of their former values. For stars the mass of our Sun, the result of the helium flash is a collapse into an orangeish-yellow star with perhaps ten times the current solar diameter and 40 times the luminosity. It is quite a comedown.

The End Of The Sun The final 140 million years or so of the Sun's life will be very complicated. After its collapse, as illustrated in Figure 1, the Sun will reestablish itself as a star with a double energy source: it will have a dense (but not electron-degenerate) carbon-oxygen core surrounded by a shell where helium is burning into carbon, and outside of that it will have another shell where hydrogen is burning into helium. (The core oxygen is created by slow fusion between carbon and helium at the core's surface. In heavier stars, the oxygen can in turn fuse with the helium to make neon.) Helium fusion produces only 9% as much energy per kilogram as hydrogen fusion, so energy-wise, the Sun continues to be mainly a hydrogen reactor. 90% of its luminosity still comes from burning hydrogen. However, it is the helium surrounding the core which now dictates how the Sun will evolve. The Sun more-or-less repeats what it did as a aging main-sequence star, except now with a carbon-helium mix in the core rather than a helium-hydrogen mix.

For a time it achieves relative stability and maintains hydrostatic equilibrium in its new incarnation as an orangeish-yellow "subgiant" star. Thus, stars in this phase of their existence are sometimes said to be on the "helium main sequence". From the fleeting perspective of a human lifetime, subgiant stars seem calm enough: the well-known bright star Arcturus, whose light was used to open the 1933 Chicago World's Fair, is such a star. It has not changed in any measurable way since the invention of the telescope. But the high temperatures necessary to maintain helium burning mean that the Sun can only burn helium one way: very fast. The hot core dictates rapid hydrogen burning as well. When it was on the normal main sequence, the Sun's luminosity held fairly close to 1.0 Lo for around nine billion years before brightening to about 2.7 Lo at the end. On the helium main sequence, the Sun's luminosity will hold at about 45 Lo before brightening to about 110 Lo at the end. Not so impressive as a red giant, but very bright nonetheless.

To maintain its subgiant lifestyle the Sun must tear through the fuel in its helium core 100 times faster than it did with its original hydrogen core. After only a hundred million years on the helium main sequence, the Sun will once again begin to climb towards the realm of the red giants, and for the same reasons as it did before. But there is no "carbon flash" equivalent of the helium flash that stopped the Sun the first time. The temperature and pressure needed to ignite carbon-carbon fusion is too great for the Sun to achieve no matter how compressed its core becomes, so the carbon just accumulates and becomes ever denser. The trend that the Sun showed on its first run as a red giant, when its core was crushed to white dwarf densities even as the outer layers billowed to tens of millions of kilometers in diameter, is unstoppable now. The Sun becomes a red giant again, this time with a peak luminosity above 3,000 Lo. Its outer layers blow further and further outward, beyond the orbit of Jupiter, even as its electron-degenerate core swiftly grows more massive and therefore smaller and more dense. And eventually the day comes when the two part company.

The final days of a star are extremely complicated, because the helium-burning and hydrogen-burning shells don't burn at the same rate. The hotter, faster-burning helium shell tends to race outwards and overtake the hydrogen-burning shell, and when that happens there is no more helium left to burn, so the helium shell fizzles out. But the giant star quickly cooks up more helium, which then collects on the white-dwarf core until it suddenly flares up in a run-away helium ignition that is something like a baby version of a helium core flash. The helium flare-up disrupts (turns off) the hydrogen burning for a short time, and so it goes. At the very end, the Sun will literally cough itself to death as multiple fuel ignitions and choked-off fusion extinguishments rip through its atmosphere. In four or five huge bursts, spaced roughly 100,000 years apart, the outer layers of the Sun will separate from the core and be completely blown away. They will form an enormous, expanding shell around the solar system, and move outward to rejoin the interstellar gas. Roughly 45% of the Sun's mass will escape in this way.

The remaining 55% of the Sun's mass is soon compressed into the white-hot, ultra-dense core. To someone watching the Sun from far away, the Sun would appear to rapidly shift colors from red to white as the gaseous veil surrounding it is lifted. (By "rapidly", of course, I mean a time span only a few times longer than the age of the pyramids.) The exposed surface of the searing solar core will be so hot, at least 170,000 K°, that it will emit more x-rays than visible light. (Post-red-giant stars are the hottest stars known, excepting neutron stars.) Its luminosity will be a brilliant 4,000 Lo. The Sun will have become a radiation source of truly galactic stature, its energy lighting up the escaping gas around it like a huge neon sign. Such clouds are called planetary nebula, a misleading name, because 18th-century astronomers could barely see them with the telescopes of the time and thought that they looked like planets. They are among the most beautiful sights in astronomy. The photograph at right, of the nebula known as NGC 6751, is of one of my favorites.

The bright spot in the center is the post-red-giant parent star. Remarkably, there is a star right at the point of blowing off its outer layers which can be seen with the naked eye. This is Mira, the "Amazing One", so named by Arabian astronomers in the Middle Ages because Mira rather erratically varies over a span of roughly 330 days from being the brightest star in its constellation (Cetus, the Whale) to total invisibility. Mira is the only classically named star that you cannot see, much of the time. Modern instruments reveal that Mira is a vastly over-extended bag of deep-red gas that is not even closely spherical and which, at 2,000 K°, is also one of the coolest stars known. Its atmosphere is undergoing complex undulations and oscillations as the nuclear burning below it sputters and gasps. Hence, its variability. In a paltry 500,000 years or less, Mira will be a planetary nebula.

As for the Sun, without its outer layers to supply it with more hydrogen, it can only maintain the gorgeous display of its nebula for a few thousand years, hardly more than a snap of the fingers by galactic standards. The last dregs of fuel on the dense core will finally burn out, and for the first time in over twelve billion years the Sun will cease to produce energy. The nebula will disperse and fade. The Sun has become a white dwarf, little larger than the Earth but 200,000 times more massive, and for billions of years to come all it will do is slowly cool off. Due to their immense density, the time it takes white dwarfs to cool off is so great that not even the oldest known (nearly 12 billion years) have had time to cool much below 5000 K°. These very old "white dwarfs" could perhaps more accurately be called "yellowish-white" dwarfs, but in any case, the Milky Way does not contain any "black dwarfs". All of the ten billion or so white dwarf stars that our galaxy has produced since the Big Bang are still shining, however dimly.

The Sun Will Eventually Engulf Earth--Maybe - Scientific American Space The Sun Will Eventually Engulf Earth--Maybe Researchers debate whether Earth will be swallowed by the sun as it expands into a red giant billions of years from now By David Appell on September 1, 2008 Credit: Lynette Cook Photo Researchers, Inc. Advertisement | Report Ad The future looks bright—maybe too bright. The sun is slowly expanding and brightening, and over the next few billion years it will eventually desiccate Earth, leaving it hot, brown and uninhabitable. About 7.6 billion years from now, the sun will reach its maximum size as a red giant: its surface will extend beyond Earth’s orbit today by 20 percent and will shine 3,000 times brighter. In its final stage, the sun will collapse into a white dwarf. Although scientists agree on the sun’s future, they disagree about what will happen to Earth. Since 1924, when British mathematician James Jeans first considered Earth’s fate during the sun’s red giant phase, a bevy of scientists have reached oscillating conclusions. In some scenarios, our planet escapes vaporization; in the latest analyses, however, it does not.

The answer is not straightforward, because although the sun will expand beyond Earth’s orbit, or one astronomical unit (AU), it will lose mass along the way. As a result, Earth should drift outward as the gravitational tug lessens over time. (At its maximum radius of 1.2 AU, the sun will have lost about one third of its mass, compared with its current heft.) In this way, Earth could escape solar envelopment. But other factors complicate the analysis. Drag on the planet from the sun’s outermost, tenuous layers will cause Earth to drift inward. Smaller forces from the other planets—all in turn reacting to the same reducing, expanding sun—are even more difficult to account for completely. Earlier this year two teams reported different kinds of calculations indicating that Earth will be swallowed up by the sun. In a calculation that would thrill any college junior studying classical mechanics, Lorenzo Iorio of Italy’s National Institute of Nuclear Physics used perturbation theory. It simplifies analyses by dropping relatively small factors, thereby making complex equations of motions that describe the interactions between the sun and Earth mathematically manageable.

Assuming that the sun’s yearly mass loss (currently about one part in 100 trillion) remains small for the duration of its evolution to the red giant phase, Iorio calculates that Earth will move outward at about three millimeters a year, or only 0.0002 AU by the sun’s red giant phase. But at that point the sun will balloon up, in only a million years, to 1.2 AU in radius, thus vaporizing Earth. Iorio’s paper, submitted to Astrophysics and Space Science, has not yet been peer-reviewed. Several scientists question whether quantities that Iorio assumes are small will indeed remain small throughout the sun’s evolution. Even if Iorio got his number crunching wrong, he may have the right answer. In an analysis published in the May Monthly Notices of the Royal Astronomical Society, Klaus-Peter Schröder of the University of Guanajuato in Mexico and Robert Smith of the University of Sussex in England also conclude that Earth is doomed, by using more exact solar models and by considering tidal interactions. As the sun loses mass and expands, its rotation rate must also slow down—physics students learn this relation as the conservation of angular momentum.

The slowed rotation causes a tidal bulge on the sun’s surface. The gravity exerted by this bulge pulls Earth inward. With such a consideration, the researchers find that any planet with a present-day orbital radius of less than 1.15 AU will ultimately perish. Could Earth be saved if someone is still left at home? In a bold piece of astronomical engineering, Don Korycansky of the University of California, Santa Cruz, and his colleagues have proposed nudging Earth with a large asteroid arranged to pass nearby periodically. It could take one billion years to move our planet out to somewhere safe, like the orbit of Mars. Our moon, though, might have to be left behind, and any miscalculation could mean extinction. Needless to say, more study is required. [break] Outer Planets Could Warm Up as Sun Dies - Universe Today Universe Today Outer Planets Could Warm Up as Sun Dies Article Updated: 24 Mar , 2012 Image credit: NASA We are doomed. One day the Earth will be a burnt cinder orbiting a swollen red star. This is the ultimate fate of any planet living close to a main sequence star like our sun.

Main sequence stars run on hydrogen, and when this fuel runs out, they switch over to helium and become a red giant. While the sun’s transition into a red giant is sad news for Earth, the icy planets in the most distant regions of our solar system will bask in the sun’s warmth for the first time. The sun has been slowly but steadily growing brighter and hotter over the course of its lifetime. When the sun becomes a red giant in about 4 billion years, our familiar yellow sun will turn a vivid red, as it mainly emits the lower frequency energy of infrared and visible red light. It will grow thousands of times brighter and yet have a cooler surface temperature, and its atmosphere will expand, slowly engulfing Mercury, Venus and possibly even the Earth. While the sun’s atmosphere is predicted to reach Earth’s orbit of 1 AU, red giants tend to lose a lot of mass, and this wave of expelled gases could push Earth just out of range. But whether the Earth is consumed or merely singed, all life on Earth will have passed into oblivion. Yet the conditions that make life possible could appear elsewhere in the solar system, according to a paper published in the journal Astrobiology by S.

Alan Stern, Director of the Southwest Research Institute’s Department of Space Studies in Boulder, Colorado. He says that planets located 10 to 50 AU will be in the red giant sun’s habitable zone. The habitable zone of a solar system is the region where water can remain in a liquid state. The habitable zone will shift gradually through the 10 to 50 AU region as the sun grows brighter and brighter, evolving through its red giant phase. Saturn, Uranus, Neptune and Pluto all lie within 10 to 50 AU, as do their icy moons and the Kuiper Belt Objects. But not all these worlds will have an equal chance at life. The prospects for habitability on the gaseous planets Saturn, Neptune and Uranus may not be affected all that much by the red giant transition. Astronomers have discovered gaseous planets orbiting very close to their parent star in other solar systems, and these “hot Jupiters” seem to hold onto their gaseous atmospheres despite their proximity to the intense radiation. Life as we know it is not likely to appear on gaseous planets.

Stern thinks Neptune’s moon Triton, Pluto and its moon Charon, and the Kuiper Belt Objects will have the best chances for life. These bodies are rich in organic chemicals, and the heat of the red giant sun will melt their icy surfaces into oceans. “When the sun is a red giant, the ice worlds of our solar system will melt and become ocean oases for tens to several hundreds of millions of years,” says Stern. “Our solar system will then harbor not one world with surface oceans, as it does now, but hundreds, for all of the icy moons of the giant planets, and the icy dwarf planets of the Kuiper Belt will also bear oceans then. Because temperature on Pluto will not be very different then, than Miami Beach’s temperature now, I like to call these worlds ‘warm Plutos,’ in analogy to the plethora of hot Jupiters found orbiting sun-like stars in recent years.” The influence of the sun is not the whole story, however – the characteristics of a planetary body go a long way toward determining habitability. Such characteristics include a planet’s internal activity, the reflectivity, or “albedo” of a planet, and the thickness and composition of the atmosphere.

Even if a planet has all the elements that favor habitability, life will not necessarily appear. “We don’t know what is needed to start life,” says Don Brownlee, an astronomer with the University of Washington in Seattle and co-author of the book, “The Life and Death of Planet Earth.” Brownlee says that if warm wet interiors and organic materials are all that’s needed, then Pluto, Triton, and the Kuiper Belt Objects could harbor life. “As a word of caution, however, the interiors of asteroids that produced the carbonaceous chondrite meteorites were warm and wet for perhaps millions of years in the early history of the solar system,” says Brownlee. “These bodies are extremely rich in both water and organic materials, and yet there is no compelling evidence that any asteroidal meteorite ever had living things in it.” A planetary body’s orbit also will affect its chances for life. Pluto, for instance, doesn’t have a nice, regular orbit like the Earth. The orbit of Pluto is comparatively eccentric, varying in distance from the sun.

From January 1979 through February 1999, Pluto was closer to the sun than Neptune, and in a hundred years, it’ll be almost twice as far out as Neptune. This type of orbit will cause Pluto to undergo extreme heating alternating with extreme cooling. Triton’s orbit, too, is peculiar. Triton is the only large moon to orbit backwards, or “retrograde.” Triton may have this unusual orbit because it formed as a Kuiper Belt Object and then was captured by Neptune’s gravity. It’s an unstable alliance, since the retrograde orbit creates tidal interactions with Neptune. Scientists predict that someday Triton will either crash into Neptune, or break up into tiny pieces and form a ring around the planet. “The timescale for the tidal decay of Triton’s orbit is uncertain, so it could be around, or it might have already crashed by the time the sun goes red giant,” says Stern. “If Triton is around, it’ll probably end up looking like the same kind of organic-rich ocean world as Pluto.” The sun will burn as a red giant for about 250 million years, but is that enough time for life to get a foothold?

During most of the red giant lifetime, the sun will be only 30 times brighter than its current state. Toward the end of the red giant phase the sun will grow more than 1,000 times brighter, and occasionally release pulses of energy reaching 6,000 times current brightness. But this period of intense brightness will last for a few million years, or tens of millions of years at most. The brevity of the red giant’s brightest phases suggests to Brownlee that Pluto doesn’t hold much promise for life. Because of Pluto’s average orbit of 40 AU, the sun would have to be 1,600 times brighter for Pluto to get the same solar radiation we currently get on Earth. “The sun will reach this brightness, but only for a very brief period of time – only a million years or so,” says Brownlee. “The surface and atmosphere of Pluto will be ‘improved’ from our point of view, but it won’t be a nice place for any significant period of time”. After the red giant phase, the sun will become fainter, and will shrink to the size of the Earth, becoming a white dwarf.

The distant planets that basked in the light of the red giant will become frozen ice worlds once again. So if life is to appear in a red giant system, it will need a quick start. Life on Earth is thought to have originated 3.8 billion years ago, some 800 million years after our planet was born. But that is probably because the planets in the inner solar system experienced 800 million years of heavy asteroid bombardment. Even if life had gotten started immediately, the early rain of asteroids would’ve wiped the Earth clean of that life. Brownlee says a new era of bombardment could begin for the outer planets, because the red giant sun could disturb the vast number of comets in the Kuiper Belt. “When the red giant sun is 1,000 times brighter, it loses almost half of its mass to space,” says Brownlee. “This causes orbiting bodies to move outward. Gas loss and other effects might destabilize the Kuiper Belt and create another period of interesting bombardment.” But Stern says that planets made habitable by a red giant sun won’t be bombarded as often as the early Earth was, because the ancient asteroid belt had much more material than the Kuiper Belt has today.

In addition, the outer planets won’t experience the same ultraviolet (UV) levels that Earth has had to endure, since red giants have very low UV radiation. The higher intensity UV of a main sequence star can be damaging to the delicate proteins and RNA strands needed for life’s origin. Life on Earth could only originate underwater, in depths protected from this light intensity. Life on Earth is therefore inextricably linked to liquid water. But who knows what sort of life might originate on planets that have no need for UV shielding? Stern thinks we should look for evidence of life on Pluto-like worlds orbiting around red giants today. We currently know of 100 million solar-type stars in the Milky Way galaxy that burn as red giants, and Stern says that all of these systems could have habitable planets within 10 to 50 AU. “It would be a good test of the time required to create life on warm, water-rich worlds,” he says. “The idea of organic-rich distant bodies getting baked by a red giant star is an intriguing one, and could provide very interesting if short-lived habitats for life,” adds Brownlee.

“But I am glad that our sun has a good margin of time left.” What’s Next While much of what we know about the outer solar system is based on distant measurements made from Earth-based telescopes, on January 2, 2004, scientists caught a close-up glimpse of a Kuiper Belt Object. The Stardust spacecraft passed within 136 kilometers of comet Wild2, an enormous snowball that spent most of its 4.6 billion-year lifetime orbiting in the Kuiper Belt. Wild2 now orbits mostly inside the orbit of Jupiter. Brownlee, who is the Principle Investigator for the Stardust mission, says that the Stardust images show fantastic surface details of a body shaped both by its ancient and recent history. Stardust images show gas and dust jets shooting off the comet, as Wild2 rapidly disintegrates in the strong solar heat of the inner solar system. To learn more about the outer solar system, we’ll need to send a spacecraft out there to investigate. In 2001, NASA selected the New Horizons mission for just such a purpose. Stern, who is the Principal Investigator for the New Horizons mission, reports that the spacecraft assembly is scheduled to begin this summer.

The spacecraft is due to launch in January 2006, and arrive at Pluto the summer of 2015. The New Horizons mission will allow scientists to study the geology of Pluto and Charon, map their surfaces, and take their temperatures. Pluto’s atmosphere also will be studied in detail. In addition, the spacecraft will visit the icy bodies in the Kuiper Belt in order to make similar measurements. the dang earth isnt gunna burn up!god will come before that. yourmomsnutz more real than most think!!!!!! PLANET X THE REAL CAUSE OF GLOBAL WARMING.2009 ASP: Biography of a Star: Our Sun's Birth, Life, and Death Biography of a Star: Our Sun's Birth, Life, and Death Just Right Depending on the size of the original lump of gas and dust, the process of stellar birth can give rise to different sorts of stars. A small lump never develops high enough pressures and temperatures to start nuclear fusion. It is doomed to remain a dark, dismal stellar wanna-be -- a so-called brown dwarf. A larger lump becomes a large star, so hot and bright that it burns itself out in a few tens of millions of years.

A lump in the middle, not too small and not too large, becomes a middling star such as the Sun. Which is good: If the Sun had been much smaller, Earth would have been a dark, dead world; much larger, and Earth would have been broiled. The middle-aged suburbanite. The Sun is a two-car-garage kind of star. Its stability and temperance make it an ideal provider for tender planets. Photo courtesy of Mount Wilson Observatory. In its early years, the Sun went through a tempestuous youth, whipping up strong winds that cleared the solar system of whatever gas had not been incorporated into a planet. But then the Sun settled down. From studying rocks, fossils, and Antarctic ice, scientists think the Sun has been brightening over time, but only slightly. And how much longer will it continue to shine? For an idea of the Sun's life expectancy, astronomers look to clusters of stars, such as one named Messier 67, which is about the same age as our Sun. By simulating the life cycles of these stars on a computer, astronomers have ascertained how long stars live.

They predict that the Sun will be able to fuse hydrogen into helium in its core at about the same rate for another 5 billion years. (What a relief!) If the Sun were a car, the gas tank would now be half full. What will happen when the Sun does run out of gas? (Hydrogen gas, that is.) Fortunately, the Sun will still have reserves of hydrogen in the layers that surround the core. The core will heat up this shell of hydrogen. When the shell gets hot enough to fuse hydrogen to helium, the release of energy will carry on there. It is as if the driver of the car poured an extra few gallons into the fuel tank. But this trick has a price. The source of energy will no longer be the dense, massive core, but rather a shell closer to the surface -- and that will make a big (so to speak) difference in the structure of the Sun. The Sun will puff up until its radius is 30 times greater. It will become a red giant, similar to the star Arcturus, though much smaller than a supergiant such as Betelgeuse (see photo on p. 3).

A red giant is red because its exterior cooled from 9,000 to 3,000 degrees Fahrenheit as it expanded; for a star, red means cool. This red-giant stage will last for about 2 billion years. That Time Bomb in the Middle The last fling. Its normal life over, Betelgeuse is now a red supergiant — red, because its surface is a comparatively cool red-hot, and supergiant, because it is hundreds of times larger than the Sun and ten times more massive. Its waistline, however, is not a sign of might, but of impending death. Photo courtesy of Andrea Dupree, Ronald Gilliland, NASA, and the European Space Agency. The striking but now-outdated video Universe, produced by NASA in the 1970s, shows the red-giant Sun engulfing the Earth. Though certainly dramatic, this is now thought to be incorrect. Astronomers have had to scale down their estimates of the size of red giants based on data from the satellite Hipparcos and from the new optical and infrared interferometers -- networks of telescopes which can take images of large, nearby stars.

Now we think the Sun will not engulf us when it becomes a red giant. But that is small comfort. In its retirement from normal core fusion, our previously nurturing star will care little for its planetary children. It will be pumping out a thousand times more energy, making Earth a good approximation to hell. To add insult to injury, the solar wind -- a stream of particles which now gives us fun things such as the aurora borealis -- will become a cyclone that will make radio communication impossible and perhaps evaporate the atmosphere altogether. Looking on the bright side, the red-giant Sun may be warm enough to melt the water-rich but now-frozen moons of Jupiter and Saturn. Humanity, if it is still around, might relocate there. Meanwhile, what happens to all that helium being produced in the shell? It gently rains onto the dead, but still toasty, core of the Sun, making the core more massive and more compressed. This raises the temperature of the core until suddenly -- and I really do mean suddenly, as in seconds -- the helium in the core fires up and begins to fuse itself into carbon. Using the fuel-tank analogy, this is as if the exhaust itself starts to burn. The end is drawing near.

Now the Sun has to rearrange its internal structure all over again, as its source of energy is once again the central core. The Sun will contract back to a bit larger than its original radius and will give off 10 times as much energy as what we are used to now. This phase only lasts another 500 million years, as there are a lot fewer helium nuclei (it took four hydrogen nuclei to make one helium nucleus, and three heliums to make one carbon) and the energy production is much less efficient. As the Sun exhausts the helium in the core, it desperately staves off the inevitable by resorting again to those reserves in its outer layers. Again the Sun expands. This time, it grows so large that its outer edge is only weakly gravitationally bound to the core. The Sun barely holds itself together anymore. This eleventh-hour attempt at life-support is pitifully ineffective; the final red-giant stage can be maintained for only 100 million years. At this point, things will really start falling apart. The Sun's outer layers, freed from the gravitational clutches of the core, will waft away.

Over the course of about 10,000 years, these layers will spread out into space as an enormous sphere of gas lit up by the now-naked hot core. These layers constitute a "planetary nebula," so called because in a small telescope the gas cloud looks a bit like the disc of a planet (see photo on p. 3). The hot core is now a "white dwarf," a stellar cinder. As a white dwarf, the ex-Sun will glow white-hot for a near-eternity. The cremation. After stars like the Sun fuse their last atom, they scatter their ashes into space as a so-called planetary nebula, such as Abell 39. At the center of the nebula is what’s left of the star: a slowly decaying “white dwarf.” Photo courtesy of George Jacoby of the National Optical Astronomy Observatories. Alas, there will be no dramatic explosions to entertain our distant descendants: The Sun would have had to start with at least eight times more mass to die the spectacular death of a supernova. The Sun, modest in life, is subdued in death.

After the planetary nebula fades, there is no nuclear fusion at all (no extra fuel, no fuel tank, not even the trunk is left), just a lump of hot carbon and some happy memories. The Sun will be well and truly dead. The sphere of gas drifts off and eventually is gathered up in a new cloud, and become part of the next generation of star formation. Perhaps one day, the ashes of the Sun will throw their lot in with another star to be born, live, die, and, perhaps, give sustenance to other warm little planets. BETH HUFNAGEL is a postdoctoral researcher at Michigan State University in East Lansing. As an auditor, she used to ferret out the secrets of corporate finance -- talents now applied to the evolution of Sun-like stars. Her email address is hufnagel@stsci.edu . George Musser contributed to this article. White Dwarfs - Introduction White Dwarfs - Introduction White Dwarfs Where do White Dwarfs Come From? Where a star ends up at the end of its life depends on the mass it was born with. Stars that have a lot of mass may end their lives as black holes or neutron stars .

A low or medium mass star (with mass less than about 8 times the mass of our Sun) will become a white dwarf. A typical white dwarf is about as massive as the Sun, yet only slightly bigger than the Earth. This makes white dwarfs one of the densest forms of matter, surpassed only by neutron stars and black holes. Black Hole Neutron Star White Dwarf Medium mass stars, like our Sun, live by fusing the hydrogen within their cores into helium . This is what our Sun is doing now. The heat the Sun generates by its nuclear fusion of hydrogen into helium creates an outward pressure. In another 5 billion years, the Sun will have used up all the hydrogen in its core. This situation in a star is similar to a pressure cooker. Heating something in a sealed container causes a build up in pressure. The same thing happens in the Sun. Although the Sun may not strictly be a sealed container, gravity causes it to act like one, pulling the star inward, while the pressure created by the hot gas in the core pushes to get out. The balance between pressure and gravity is very delicate. When the Sun runs out of hydrogen to fuse, the balance tips in the favor of gravity, and the star starts to collapse.

But compacting a star causes it to heat up again and it is able fuse what little hydrogen remains in a shell wrapped around its core. (Betelgeuse) January 15, 1996, Hubble Space Telescope Captures First Direct Image of a Star, A. Dupree (CfA) and NASA. This burning shell of hydrogen expands the outer layers of the star. When this happens, our Sun will become a red giant ; it will be so big that Mercury will be completely swallowed! When a star gets bigger, its heat spreads out, making its overall temperature cooler. But the core temperature of our red giant Sun increases until it's finally hot enough to fuse the helium created from hydrogen fusion. Eventually, it will transform the helium into carbon and other heavier elements . The Sun will only spend one billion years as a red giant, as opposed to the nearly 10 billion it spent busily burning hydrogen. We already know that medium mass stars, like our Sun, become red giants. But what happens after that? Our red giant Sun will still be eating up helium and cranking out carbon. But when it's finished its helium, it isn't quite hot enough to be able to burn the carbon it created.

What now? Since our Sun won't be hot enough to ignite the carbon it its core, it will succumb to gravity again. When the core of the star contracts, it will cause a release of energy that makes the envelope of the star expand. Now the star has become an even bigger giant than before! Our Sun's radius will become larger than Earth's orbit ! The Sun will not be very stable at this point and will lose mass. This continues until the star finally blows its outer layers off. The core of the star, however, remains intact, and becomes a white dwarf. The white dwarf will be surrounded by an expanding shell of gas in an object known as a planetary nebula . They are called this because early observers thought they looked like the planets Uranus and Neptune. There are some planetary nebulae that can be viewed through a backyard telescope. In about half of them, the central white dwarf can be seen using a moderate sized telescope. Planetary nebulae seem to mark the transition of a medium mass star from red giant to white dwarf. Stars that are comparable in mass to our Sun will become white dwarfs within 75,000 years of blowing off their envelopes.

Eventually they, like our Sun, will cool down, radiating heat into space and fading into black lumps of carbon. It may take 10 billion years, but our Sun will someday reach the end of the line and quietly become a black dwarf . White dwarfs can tell us about the age of the Universe. If we can estimate the time it takes for a white dwarf to cool into a black dwarf, that would give us a lower limit on the age of the Universe and our galaxy . But because it takes billions of years for white dwarfs to cool, we don't think the universe is old enough yet for many, if any, white dwarfs to have become black dwarfs. Finding black dwarfs would certainly alter our understanding of the cooling process in white dwarfs. Observations of White Dwarfs The arrow is pointing to white dwarf, Sirius B, next to the large Sirius A. There are several ways to observe white dwarf stars. The first white dwarf to be discovered was found because it is a companion star to Sirius, a bright star in the constellation Canis Major. In 1844, astronomer Friedrich Bessel noticed that Sirius had a slight back and forth motion, as if it was orbiting an unseen object.

In 1863, the optician and telescope maker Alvan Clark spotted this mysterious object. This companion star was later determined to be a white dwarf. This pair are now referred to as Sirius A and B, with B being the white dwarf. The orbital period of this system is about 50 years. Since white dwarfs are very small and thus very hard to detect, binary systems are a helpful way to locate them. As with the Sirius system, if a star seems to have some sort of unexplained motion, we may find that the single star is really a multiple system. Upon close inspection we may find that it has a white dwarf companion. The Hubble Space Telescope, with its 2.4 meter mirror and advanced optics, has been successfully viewing white dwarfs with its Wide Field and Planetary Camera. In August of 1995, this camera observed more than 75 white dwarfs in the globular cluster M4 in the constellation Scorpius. These white dwarfs were so faint that the brightest of them was no more luminous than a 100 watt light bulb seen at the moon's distance.

M4 is located 7,000 light years away but is the nearest globular cluster to Earth. It is also approximately 14 billion years old, which is why so many of its stars are near the end of their lives. Optical Image (left) and a portion of the Hubble Space Telescope observation (right) of the globular cluster M4. The white dwarfs are circled in the HST image. ROSAT image of HZ 43 Optical telescopes are not the only way to view white dwarfs. The white dwarf HZ 43 was observed by the X-ray satellite ROSAT . X-rays come from inside the visible surface of the white dwarf. This region is very dense and can be as hot as 100,000 degrees in a very young white dwarf. A white dwarf's outer layers contain just helium and hydrogen and so are essentially transparent to the X-rays that are emitted by the much hotter inner layers.

Last Modified: December 2006 The above images of Betelgeuse and M4 were created with support to Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., from NASA contract NAS5-26555, grant number STScI-PRC96-04, and are reproduced with permission from AURA/STScI. The two planetary nebulae images are courtesy of Bruce Balick and Jay Alexander, University of Washington, Arsen Hajian, U.S. Naval Observatory, Yervant Terzian, Cornell University, Mario Perinotto and Patrizio Patriarchi, Observatorio Arcetri (IT) The image of Sirius A and B is courtesy of Lick Observatory. A service of the High Energy Astrophysics Science Archive Research Center ( HEASARC ), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA / GSFC

Question: What is the sun likely to end up as after the red giant phase
Answer: White dwarf